The long-term goal of this project is to understand the adaptive mechanisms underlying control of spatial orientation in stance and gait in order to ameliorate balance and gait disorders. Altered surface conditions often result in falls and instability in patients with neurological or vestibular deficits and the elderly. We aim to better understand how the nervous system adapts postural alignment and locomotor trajectory to inclined and moving surfaces. Work in our current grant cycle has shown that adaptation to altered support surfaces during stance and locomotion results in long-lasting kinesthetic after-effects. The proposed studies will examine the central and sensory recalibration mechanisms for adaptation of postural alignment and locomotor trajectories and the role of the cerebellum in this adaptation. We hypothesize that these postural and locomotor after-effects of exposure to altered surfaces reflect a slowly changing, central representation of kinesthetic trunk-to-surface spatial orientation. Our specific aims are: Specific Aim I: To identify similarities among mechanisms responsible for adapting postural alignment and locomotor trajectory. We hypothesize that the CMSuses a common mechanism to adapt postural and locomotor orientation on changing surfaces such that each individual's ability to adapt posture for changes in surface inclination will be correlated with their ability to adapt locomotion for changes in surface conditions. We also hypothesize that both postural and locomotor after-effects of adaptation can be increased with repeated exposure to surface inclinations or rotations. Specific Aim II: To determine the roles of the cerebellum and vestibular systems in adapting stance postural alignment to changes in surface inclination. We hypothesize that the cerebellum is critical for adapting postural orientation to altered surface inclinations and the vestibular system provides an important reference for upright posture when the surface is inclined. Specific Aim III: To clarify the mechanisms underlying coordination and adaptive modulation of curvature in the locomotor trajectory. We hypothesize that turning during locomotion is controlled by regulating the ratio of angular to linear central programs for leg-trunk condition. These studies provide a new conceptual framework to understanding how the nervous system adapts spatial orientation so that novel clinical rehabilitation strategies can be developed to improve control of balance and gait.